The present invention relates to a rubber product which has similar steretchability to the human skin, so that it is suitable for applying to items to be put into contact with the human skin.
Rubber products to be applied to items being put into contact with the human skin, such as diapers, napkins, gloves, masks, and clothing including socks, underclothing and the like, are conventionally made up from natural rubber. The rubber products as above are required to be as follows.
i) The rubber product should have such steretchability similar to the human skin that the rubber product exhibits desirable adhesion properties and sealing properties without causing poor blood circulation. That is, the rubber product should be provided with such good rubber properties that the rubber product is expanded and contracted by a small force corresponding to expansion and contraction of the skin to keep its moderate tightness, and it springs back to the original form when the force is removed.
ii) The rubber product should have no allergenic ingredient, so that the rubber product prevents such problems as inflammation even when it is put into direct contact with the human skin.
iii) The rubber product should be excellent in stretchability and processability, and should have no temperature dependence. Furthermore, the rubber product should maintain its quality for a long time without being affected by the environment of usage thereof.
However, the rubber product having similar steretchability to the human skin has not been developed. Since conventional rubber product can not sufficiently follow up expansion and contraction of the human skin because of its large stretching stress, the rubber product might not sufficiently exhibit the adhesion properties and the sealing properties in some product designs. In the meantime, when the rubber product is too tight, it is unfit and inhospitable to a user, and, if too far, causes poor blood circulation.
JIS K637 specifies a standard of properties of a rubber thread wherein the thread has tensile strength of equal to or more than 150 kgf/cm2 (1.47xc3x97107 Pa), extension of equal to or more than 60%, and elongation set of equal to or less than 13%, provided modulus at 300% is equal to or less than 25 kgf/cm2 (2.45xc3x97106 Pa). The rubber thread of the standard cannot be provided with such good properties that it sufficiently follows up expansion and contraction of the human skin.
The conventional rubber product might cause inflammation when it is put into direct contact with the skin, because it is mainly composed of natural rubber which contains the allergenic ingredients protein). Therefore, the rubber product might be used with a cover made up from unwoven fabrics and the like, but in this case the covering material raises the processing cost of the rubber product and spoils the performance proper to the rubber.
While such elastic materials as thermoplastic elastomer (TPE) are provided as those materials which are applied to items to be put into direct contact with the skin, these materials are inferior in processability and setability, and have high temperature dependence, hence the materials cannot achieve steady stretching properties.
It is an object of the present invention to overcome problems in the prior art described above and to provide a rubber product which has similar stretchability to that of the human skin, so that it is suitable for application to items to be put into contact with the human skin.
A rubber product of the present invention is provided with 200% modulus M200 of equal to or less than 15 kgf/cm2 (14.7xc3x97105 Pa), preferably of equal to or less than 10 kgf/cm2 (9.8xc3x97105 Pa), and modulus ratios of 200% modulus (M200) to 100% modulus (M100) M200/M100, 300% modulus (M300) to 200% modulus (M200) M300/M200, and 400% modulus (M400) to 300% modulus (M300) M400/M300 all of which are equal to or less than 2.0, particularly equal to or less than 1.5.
The rubber product provided with such a low modulus and law modulus ratios, as M200xe2x89xa615 kgf/cm2 (14.7xc3x97105 Pa), M200/M100xe2x89xa63.0, M300/M200xe2x89xa63.0 and M400/M300xe2x89xa62.0 acquires the stretchability similar to that of the human skin.
The rubber product having such modulus as above is provided with tensile property as illustrated with the solid line in FIG. 1, and the rubber product having such tensile properties can acquire the stretchability exceptionally similar to that of the human skin. In FIG. 1, the broken line illustrates the tensile property of the conventional rubber thread used for the usual disposal diaper, and it shows that the rubber thread has stretchability seriously dissimilar from the human skin, so it is difficult to achieve enough adhesion properties and sealing properties without causing poor blood circulation by its too large tightness. The conventional rubber thread has 200% modulus M200 of more than 15 kgf/cm2 and the aforementioned modulus ratios of more than 2.0.
Since the rubber product of the present invention is easily deformed with a small load, it is required to have breaking extension of equal to or more than 600%, particularly of equal to or more than 800% from the viewpoint of the handling of the products. And the rubber product is preferable to have elongation set of equal to or less than 12% in order to maintain the sealing properties for a long time.
The rubber product of the present invention is preferable not to contain allergenic ingredients, that is, the rubber product is preferable to consist of synthetic rubber other than natural rubber, particularly of synthetic isoprene rubber (IR), more particularly IR containing equal to or more than 90% cis-1,4 links.
The rubber product of the present invention is preferable to have specific gravity of equal to or less than 1.06, particularly equal to or less than 1.0 in order to achieve a low modulus, low modulus ratios, and low elongation set.
From the viewpoint of security for durability, it is desirable that the rubber product is free from cracking even when it is held at extension of 20% for more than one month.